Many users of devices attaching to and accessing cellular networks enter into service contracts with cellular service providers that permit use during a given time period of a specified quantity of voice minutes, messages and/or data for a set fee. Subscribers to cellular networks often are in a position where either they expect that they will not use some of the purchased capacity within the given time period, resulting in wasted money, or they will go over the permitted amounts and need to purchase excess plan capacity at high overage rates charged by cellular service providers. Accordingly, there is a need for a method and system that would allow a subscriber to either sell its excess capacity or selectively buy additional capacity on a real time basis. The method and system should be cost effective, efficient and adaptable to existing environments. The present invention addresses such a need.